MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY
APRIL, 2005
(For general comments about the nature of these summaries, as well as
information on how to download the tabular cyclone track files, see
the Author's Note at the end of this summary.)
*************************************************************************
APRIL HIGHLIGHTS
--> Two tropical cyclones in South Indian Ocean
--> Strong typhoon recurves east of Philippines
*************************************************************************
***** Feature of the Month for April *****
REVIEW OF GLOBAL TROPICAL CYCLONE TERMINOLOGY
This month's feature is a repeat from several years back, last being
included in the April, 2001, monthly summary. I have updated a few
items based upon changes in basic definitions.
The following is a synopsis of the operational terminology used by
the various TCWCs to describe the different stages of tropical cyclone
development and intensification. This gives the formal terminology
used to refer to a given cyclone in warnings and advisories. For
example, the Saffir/Simpson category is widely utilized in the U. S.
to describe a hurricane's intensity, but the advisories do not refer
to a hurricane formally as "Category Four Hurricane Xerxes" in the
title line of the advisories. Also, in the U. S. the adjective
"severe" may be frequently used to describe the character of a
hurricane, but is not formally used as the descriptor for a given
cyclone intensity range as it is in some basins.
1. ATLANTIC and NORTHEAST PACIFIC Basins - TPC/NHC (also CPHC)
MSW Averaging Period: 1 minute
Tropical Cyclone - generic term for systems of all intensities
Tropical Disturbance - distinct area of disturbed weather but
usually with no well-defined low-level circulation apparent/
regular advisories not issued/ usually corresponds to Dvorak
ratings less than T2.0
Tropical Depression - fairly well-defined low-level circulation/
MSW less than 34 kts/ Dvorak rating usually T2.0
Tropical Storm - MSW in range of 34-63 kts/ Dvorak rating T2.5,
T3.0, or T3.5
Hurricane - MSW exceeding 63 kts/ Dvorak rating T4.0 or higher
The point at which regular advisories are initiated is a little
subjective. A system with a Dvorak rating of T1.5 might be upgraded
to a tropical depression if it were in a position to affect a populated
area and/or if it seemed to be rapidly intensifying and its development
potential was considered excellent.
2. JTWC for NORTHWEST PACIFIC Basin Only
MSW Averaging Period: 1 minute
Tropical Cyclone - generic term for systems of all intensities
Tropical Disturbance - distinct area of disturbed weather but
usually with no well-defined low-level circulation apparent/
regular advisories not issued/ usually corresponds to Dvorak
ratings of T1.0 or less/ MSW generally less than 25 kts
Tropical Depression - fairly well-defined low-level circulation/
MSW 25-34 kts/ Dvorak rating usually T1.5 - T2.0
Tropical Storm - MSW in range of 34-63 kts/ Dvorak rating T2.5,
T3.0, or T3.5
Typhoon - MSW exceeding 63 kts/ Dvorak rating T4.0 or higher
Super typhoon - MSW reaching or exceeding 130 kts
3. JTWC for NORTH INDIAN OCEAN and SOUTHERN HEMISPHERE
MSW Averaging Period: 1 minute
For the North Indian Ocean and all Southern Hemisphere regions, JTWC
uses only the generic term "Tropical Cyclone" to refer to systems of all
intensities in warning status. Warnings are usually initiated when the
system is forecast to produce gale/tropical storm force winds within
48 hours. In many cases winds are already approaching this threshold
when the first warning is issued and frequently the initial MSW is set
at 35 kts.
4. NORTHWEST PACIFIC Basin - JMA (Japan)
MSW Averaging Period: 10 minutes
Tropical Cyclone - generic term for systems of all intensities
Low-pressure Area - distinct area of disturbed weather but
usually with no well-defined low-level circulation apparent/
regular warnings not issued
Tropical Depression - fairly well-defined low-level circulation/
MSW less than 34 kts
Tropical Storm - MSW in range of 34-47 kts/ Dvorak rating T2.5
or T3.0
Severe Tropical Storm - MSW in range of 48-63 kts/ Dvorak rating
T3.5 or T4.0
Hurricane - MSW exceeding 63 kts/ Dvorak rating T4.5 or higher
The Japanese Meteorological Agency (JMA) is the World Meteorological
Organization's (WMO) official Regional Specialised Meteorological
Centre (RSMC) for the Northwest Pacific Basin. While adhering to
a 10-min averaging period for MSW, JMA normally equates 34 kts to a
Dvorak rating of T2.5; thus, JMA and JTWC agree in principle on the
threshold of tropical storm intensity. However, for very intense
typhoons, JMA's MSW estimates are usually far below those assigned
by JTWC due to a much lower 1-min to 10-min conversion factor for
extreme intensities. Other Asian nations' weather services issue
tropical cyclone warnings for portions of the Northwest Pacific region,
including the Philippines, Hong Kong, China, Vietnam, Taiwan, and
Korea. Warnings from these weather services are issued independently
of JMA but utilize the same terminology and are usually reasonably
close to JMA's positions and intensity estimates.
5. NORTH INDIAN OCEAN Basin - IMD (Indian Meteorological Department)
MSW Averaging Period: 1 minute
Low-pressure Area - weak, diffuse area of low pressure without
a definite surface circulation
Depression - well-defined low-level circulation but with MSW
generally less than 28 kts/ Dvorak rating of T1.5
Deep Depression - depression with MSW in range of 28-33 kts/
Dvorak rating of T2.0
Cyclonic Storm - tropical cyclone with MSW in range of 34-47 kts/
Dvorak rating T2.5 - T3.0
Severe Cyclonic Storm - tropical cyclone with MSW in range of
48 - 63 kts/ Dvorak rating of T3.5
Very Severe Cyclonic Storm - tropical cyclone with MSW exceeding
63 kts / Dvorak rating T4.0 or higher
The Indian Meteorological Department (IMD) is the WMO's RSMC for
the North Indian Ocean (Bay of Bengal and Arabian Sea), although the
meteorological services of other nations may also issue warnings for
portions of the basin.
NOTE: Although not formally defined, IMD used the term "superstorm"
to describe the very intense Tropical Cyclone 05B in October, 1999,
which, based upon JTWC's warnings, peaked at 140 kts.
6. SOUTHWEST INDIAN OCEAN Basin (West of 90E)
MSW Averaging Period: 10 minutes
Zone of Disturbed Weather - term used to describe weak, ill-defined
systems with winds generally less than 25 kts and corresponding
to Dvorak ratings of less than T2.0
Tropical Disturbance - MSW usually 25 kts near center/ Dvorak
rating usually T2.0 (Beaufort Force 6) / such systems usually
classified as tropical depressions by most TCWCs
Tropical Depression - MSW in range of 28-33 kts (Beaufort Force 7 -
Dvorak T2.5)
Moderate Tropical Storm - MSW in range of 34-47 kts/ Dvorak rating
of T3.0 - weak T3.5
Severe Tropical Storm - MSW in range of 48-63 kts/ Dvorak rating
of strong T3.5 - T4.0
Tropical Cyclone - MSW in range of 64-89 kts/ Dvorak rating of
T4.5 - T5.5
Intense Tropical Cyclone - MSW in range of 90-115 kts/ Dvorak
rating T6.0 - T6.5
Very Intense Tropical Cyclone - MSW exceeding 115 kts/ Dvorak
rating T7.0 - T8.0
The WMO's RSMC for the South Indian region is Meteo France on the
French island of La Reunion; however, names are actually assigned by the
Sub-regional Tropical Cyclone Advisory Centres on Mauritius (east of 55E)
and Madagascar (west of 55E). The La Reunion TCWC employs a conversion
factor of 0.88 to convert the 1-minute MSW Dvorak scale to an equivalent
10-minute average scale. (Prior to the 1999-2000 season, the conversion
factor used was 0.80.)
7. AUSTRALIAN REGION (longitude 90E eastward to longitude 160E)
MSW Averaging Period: 10 minutes
Tropical LOW - term is used to describe disturbances ranging from
diffuse, ill-defined low-pressure areas all the way to well-
organized tropical depressions with MSW up to 33 kts
Tropical Cyclone - MSW in range of 34-63 kts/ Dvorak rating ranging
from a strong T2.5/weak T3.0 to T4.0
Severe Tropical Cyclone - MSW exceeding 63 kts/ Dvorak T4.5 or
higher
Warnings in the Australian Region are issued by three separate TCWCs
at Brisbane (Queensland), Perth (Western Australia), and Darwin
(Northern Territory) with Darwin being the RSMC for the region. In
addition to these, a TCWC at Port Moresby, Papua New Guinea (formerly
an Australian territory) issues warnings for a small portion of the
region near and east of the island of New Guinea. The Papua New
Guinea region has an extremely low incidence of tropical cyclone
occurrences. The Australian centres avoid use of the term "tropical
depression" in public advices primarily to reduce possible confusion
with the use of the term "depression" in association with extratropical
systems; and also possibly because until recently (early 1990's), in
the Southwest Indian Ocean Basin, a "tropical depression" meant any
system with winds up to 63 kts (hurricane force). The Australian TCWCs
utilize a conversion factor of 0.88 or 0.90 to modify the 1-minute
Dvorak scale to an equivalent 10-minute average scale.
8. SOUTH PACIFIC Basin (east of longitude 160E)
MSW Averaging Period: 10 minutes
Tropical Disturbance - distinct area of disturbed weather but
usually with no well-defined low-level circulation apparent/
regular advisories not issued/ usually corresponds to Dvorak
ratings less than T2.0
Tropical Depression - fairly well-defined low-level circulation/
MSW less than 34 kts/ Dvorak rating usually T2.0 or weak T2.5
Tropical Cyclone - MSW exceeding 33 kts/ Dvorak rating of
strong T2.5/T3.0 or higher
The TCWC at Nadi, Fiji, is the RSMC for the South Pacific basin
but the meteorological service of New Zealand (Wellington) issues
warnings for systems that move (or very rarely form) south of latitude
25S. The Fiji TCWC employs a 1-minute to 10-minute MSW conversion
factor of 0.90 when adjusting the Dvorak scale.
NOTE: A tropical system can have associated gales and still be
classified as a tropical depression if the gales are well-removed
from the center. In such cases the gales are usually found in only
one or two quadrants. Prior to 2000, the WMO Region V definition
of a tropical cyclone required that gales surround the center, but
that definition was changed to allow classification as a tropical
cyclone if gales were present near the center and likely to persist,
even if in only one quadrant.
*************************************************************************
ACTIVITY BY BASINS
ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico
Activity for April: No tropical cyclones
Atlantic Tropical Activity for April
------------------------------------
As would be expected, there were no tropical or subtropical cyclones
during April. However, there was a system off the Carolina coastline in
mid-April which gave hints of possibly evolving into a subtropical
system. I'll describe this system by quoting three e-mails I received
pertaining to its development. In the early afternoon of 15 April Matt
Crowther wrote: "Looks like we may have a second April subtropical storm
in three years (Ana was in 2003). Sat pics show a tight circulation with
some convection near the center southeast of North Carolina."
Shortly afterward Brian McNoldy replied: "Yeah, I'd agree. I've been
watching this all day, and the increased centralized convection is indeed
very interesting. Certainly subtropical, and any tropical development
would be hard to come by, but still not bad for April. The latest
ascending QuikScat pass shows some "clean" (not rain-flagged) winds of
25-35 kts, depending on the quadrant you look at. It's sitting right
over the Gulf Stream with SSTs of around 21-22 C, but the outflow temp
is cooler than normal too, so keep that in mind."
However, early on the morning of 16 April David Roth wrote: "It
looked slightly promising yesterday, but all I'm seeing on the morning
visible imagery is a textbook occluded cyclone near 31.8N/70.3W with
maybe a few showers near the center. Sometimes synoptic-scale LOWs
will pick up some convection as they pass over the Gulf Stream. These
things happen."
*************************************************************************
NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180
Activity for April: No tropical cyclones
*************************************************************************
NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180
Activity for April: 1 tropical depression **
1 typhoon
** - classified as a tropical depression by JMA only
Sources of Information
----------------------
Most of the information presented below is based upon tropical
cyclone warnings and significant tropical weather outlooks issued
by the Joint Typhoon Warning Center of the U. S. Air Force and
Navy (JTWC), located at Pearl Harbor, Hawaii. In the companion
tropical cyclone tracks file, I normally annotate track coordinates
from some of the various Asian warning centers when their center
positions differ from JTWC's by usually 40-50 nm or more. All
references to sustained winds imply a 1-minute averaging period
unless otherwise noted.
Michael V. Padua of Naga City in the Philippines, owner of the
Typhoon 2000 website, normally sends me cyclone tracks based upon
warnings issued by the Japanese Meteorological Agency (JMA) and the
Philippine Atmospheric, Geophysical & Astronomical Services
Administration (PAGASA). Also, Huang Chunliang of Fuzhou City, China,
sends data taken from synoptic observations around the Northwest
Pacific basin. A very special thanks to Michael and Chunliang for
the assistance they so reliably provide.
In the title line for each storm I have referenced all the cyclone
names/numbers I have available: JTWC's depression number, the
JMA-assigned name (if any), JMA's tropical storm numeric designator,
and PAGASA's name for systems forming in or passing through their
area of warning responsibility.
Northwest Pacific Tropical Activity for April
---------------------------------------------
Two tropical cyclones formed in the Northwest Pacific basin during
the month of April: a typhoon of major intensity and a weak tropical
depression. The tropical depression was not recognized by JTWC nor by
any of the Asian warning agencies bar JMA and the Central Weather Bureau
of Taiwan (CWBT). JMA estimated the MSW at 30 kts, whereas CWBT does
not normally make wind estimations for tropical depressions. The system
was classified as a tropical depression by JMA only on 18 April as it
sat essentially stationary near 7.0N/140.0E, or several hundred miles
south-southwest of Guam. A "track" for this system was included in the
companion cyclone tracks file prepared by the author, and a graphic
displaying the location of this depression may be found at the following
link:
http://www.tropicalcyclone2005.com/database/tc_besttracks_graphics/PACIFIC_WEST/2005_0ATD.gif>
According to information sent by Huang Chunliang, Yap (WMO 91413,
9.48N/138.08E) picked up 127.0 mm of rainfall during the pre-depression
stages of this system between 13/0600 and 14/0600 UTC.
The other tropical cyclone of April was Typhoon Sonca (known in the
Philippines as Bising). This typhoon followed a rather long trajectory
from well east of Palau northwestward, then westward, eventually
recurving a few hundred miles east of the central Philippines. Sonca
was an impressive typhoon, reaching an intensity of 115 kts (per JTWC).
A report on this cyclone, authored by Kevin Boyle, follows.
TYPHOON SONCA
(TC-03W /TY 0503 / BISING)
20 - 29 April
----------------------------------------------
Sonca: contributed by Vietnam, is a singing bird known for its beautiful
twittering sound and which lives in mountainous areas
A. Introduction
---------------
Typhoon Sonca became the surprise package of April, 2005, in the
Western North Pacific, unexpectedly reaching a maximum intensity of
115 kts nearly 600 nm or so east of the Philippines. This storm well
illustrates the unpredictability of tropical cyclones. Typhoon Sonca
followed a track similar to that of Super Typhoon Sudal last year, but
stayed well away from Yap Island. This is the third consecutive year
in which April has produced a major typhoon with a MSW > 100 kts.
B. Storm Origins
----------------
Two suspect areas were being monitored in JTWC's STWO at 2000 UTC
16 April, one producing thunderstorm activity approximately 170 nm east-
southeast of Palau while the second, pre-Sonca, disturbance was located
85 nm south-southwest of Chuuk. As the first was initially considered
the more likely to develop into a tropical cyclone, a TCFA was issued at
18/0030 UTC. However, no further development occurred and the TCFA was
cancelled at 19/0030 UTC. (This system was the one classified as a
tropical depression by JMA on 18 April. See introductory paragraphs
above.) The system had dissipated altogether by 19/0600 UTC. Meanwhile,
the pre-Sonca LOW had been raised to a 'fair' development potential at
18/2200 UTC. An upper-level analysis depicted a low to moderate wind
shear environment with favourable outflow aloft. When multi-spectral
satellite imagery revealed convection organizing over a LLCC, a TCFA was
released at 20/0530 UTC. This was replaced by the first warning at
20/1200 UTC, placing the centre of the newly formed tropical depression
270 nm east-southeast of Yap.
C. Synoptic History
-------------------
At 1200 UTC 20 April Tropical Depression 03W was drifting westwards
at 7 kts along the southwestern periphery of the mid-level steering ridge
situated to the northeast. The storm showed little signs of developing
into a tropical storm and remained a very slack, disorganized system
during the 21st. Forecasts called for slow strengthening, but as this
didn't seem forthcoming, JTWC intended the 22/0000 UTC warning to be the
last. Just as this final statement was being released, TD-03W underwent
a redevelopment phase and satellite images at this time showed that
TD-03W had actually become much better organized. Realizing this, JTWC
was forced to reinstate the storm only six hours after the last statement
was issued so there was no break in transmission. There was a little
intensification on the 22nd but the system remained at tropical
depression status. After crossing into PAGASA's AOR at 22/1200 UTC, the
name Bising was assigned by that agency for local use.
Tropical Depression 03W finally became a named tropical storm at 0000
UTC 23 April after both JTWC and JMA upgraded their respective MSW
estimates to 35 kts. The newly-christened Sonca was then centered
approximately 375 nm west-northwest of Yap. It was at this point that
Tropical Storm Sonca really began to take off. An unexpected rapid
strengthening phase ensued, and after a 23/1633 UTC AMSR-E microwave pass
depicted a developing eye, Sonca was upgraded to a 75-kt typhoon at
23/1800 UTC while located about 450 nm west-northwest of Yap. After
moving rather erratically on a west to northwest track for a couple of
days, the storm turned north-northwestward and slowly moved in that
direction awhile before veering northwards. Its intensity continued to
climb alarmingly, reaching a peak of 115 kts at 24/1800 UTC. At this
point, Sonca was located approximately 570 nm east of Manila and was
beginning to recurve around the subtropical ridge.
(Editor's Note: The peak MSW assigned by JMA was 85 kts with an estimated
minimum CP of 940 mb. PAGASA and the CWB of Taiwan also estimated the
peak winds at 85 kts (10-min avg), whereas NMCC's was slightly higher at
90 kts.)
Even as Typhoon Sonca reached its maximum intensity at 1800 UTC
24 April, increasingly hostile environmental conditions were already
distorting the appearance of the system. Its eye soon became cloud-
filled at 25/0000 UTC and deep convection began to decrease in the
western and southern quadrants. Sonca remained a major typhoon through
the 25th until the MSW fell below 100 kts at 26/0600 UTC. The system
began to accelerate northeastward into the mid-latitude westerlies and
started to take on extratropical characteristics. At 26/1800 UTC Sonca
was downgraded to a 55-kt tropical storm only 45 nm west-northwest of
Iwo Jima, the island lying within the radius of 34-kt winds. JTWC issued
their final warning at this time, but JMA maintained Sonca as a 65-kt
typhoon. The latter agency finally classified the system as extra-
tropical at 1200 UTC on 27 April with the 45-kt gale center located about
500 nm east-northeast of Iwo Jima and moving rapidly eastward. The final
reference to former Typhoon Sonca in JMA's High Seas Bulletins was at
0000 UTC on 29 April and placed the weakening 25-kt LOW about 600 nm
north of Wake Island.
A graphic depicting the track of Typhoon Sonca may be found at the
following link:
http://www.tropicalcyclone2005.com/database/tc_besttracks_graphics/PACIFIC_WEST/2005_03W_BT.GIF.gif>
D. Meteorological Observations
------------------------------
The only meteorological observations available were sent by Huang
Chunliang--a couple of rainfall amounts from Chuuk, and these were from
the formative stages of Sonca, several days before the depression stage
began on 20 April.
Only 24-hr amount(s) >= 100 mm listed:
CHUUK, ECI (7.45N 151.83E) 116.1 mm [15/18-16/18Z]
CHUUK, ECI (7.45N 151.83E) 102.6 mm [16/00-17/00Z]
E. Damage and Casualties
------------------------
There were no known damage or casualties associated with Typhoon
Sonca.
(Report written by Kevin Boyle)
*************************************************************************
NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea
Activity for April: No tropical cyclones
*************************************************************************
SOUTHWEST INDIAN OCEAN (SWI) - South Indian Ocean West of Longitude 90E
Activity for April: 1 severe tropical storm
1 very intense tropical cyclone **
** - system formed east of 90E in Australian Region
Sources of Information
----------------------
The primary sources of tracking and intensity information for
Southwest Indian Ocean tropical cyclones are the warnings issued by
the Tropical Cyclone Warning Centre on La Reunion Island, part of
Meteo France (MFR), and the Regional Specialised Meteorological Centre
for the basin. However, tropical cyclones in this region are named
by the Sub-regional Tropical Cyclone Advisory Centres in Mauritius and
Madagascar with longitude 55E being the demarcation line between their
respective areas of naming responsibility. The La Reunion centre only
advises these agencies regarding the intensity of tropical systems.
References to sustained winds imply a 10-minute averaging period unless
otherwise stated.
In the companion tropical cyclone tracks file, I occasionally
annotate positions from warnings issued by the Joint Typhoon Warning
Center (JTWC) of the U. S. Air Force and Navy, located at Pearl
Harbor, Hawaii, when they differ from MFR's coordinates by usually
40-50 nm or more. The JTWC warnings are also the source of the
1-minute average maximum sustained wind values included in the
tracks file. Additionally, information describing details of
satellite imagery and atmospheric circulation features included in
the narratives is often gleaned from the JTWC warnings.
Southwest Indian Ocean Tropical Activity for April
--------------------------------------------------
Two tropical systems stirred Southwest Indian Ocean waters during the
month of April. Severe Tropical Storm Isang formed slowly in the eastern
part of the region early in the month and followed a poleward trajectory
through the central Indian Ocean, passing several hundred miles east of
Rodrigues Island. Isang remained weak for most of its life, intensifying
into a severe tropical storm only after reaching subtropical latitudes
and encountering the westerlies. The system may have briefly reached
tropical cyclone (i.e., hurricane) intensity shortly before becoming
extratropical.
The other system was a visitor, having formed in the Australian
Region, but was one of the most intense tropical cyclones in the South-
west Indian Ocean during the 2004-2005 season. Christened Adeline by
BoM Perth on 3 April near the Cocos Islands, the system moved westward,
reaching hurricane intensity on the 4th before crossing 90E into MFR's
region of warning responsibility on the 5th. The storm then became
Tropical Cyclone Juliet and reached a peak intensity of 120 kts as it
recurved less than 200 nm east of Rodrigues Island.
A report on Severe Tropical Storm Isang follows. A report on Tropical
Cyclone Adeline-Juliet can be found in the next section of this summary
covering the Northwest Australia/Southeast Indian Ocean region.
SEVERE TROPICAL STORM ISANG
(MFR-17 / TC-25S)
29 March - 7 April
-----------------------------------------------
Isang: contributed by Botswana
A. Storm Origins
----------------
Severe Tropical Storm Isang was a system which spent the first half
of its life as a rather weak tropical disturbance. Furthermore, after
it had been named, Isang remained a minimal tropical storm until it had
moved into the subtropics and was approaching the westerlies. At the
last possible moment the system strengthened suddenly into a severe
tropical storm, then quickly became extratropical.
An area of convection formed and persisted approximately 800 nm east-
southeast of Diego Garcia on 29 March. Deep convection was beginning to
consolidate around a LLCC, and enhanced water vapor imagery showed that
outflow was improving in the equatorward direction. An upper-level
analysis indicated that the LLCC was located in an environment of
moderate to high vertical shear and increasing 850-mb vorticity. MFR
initiated bulletins on the developing system at 1800 UTC on 29 March,
numbering it as Tropical Disturbance 17. The broad center was then
located roughly 750 nm east-southeast of Diego Garcia. JTWC issued a
TCFA at 0200 UTC on the 30th after satellite imagery revealed an increase
in deep convection and the formation of a possible CDO. However, only
seven hours later the TCFA was cancelled after the LLCC was shown to have
become fully-exposed with the deep convection located approximately
150 nm west of the LLCC.
MFR maintained the disturbance as a 25-kt system for the next few days
as it moved slowly and erratically on a generally west-southwesterly
course. The organization of the system apparently fluctuated during this
time as JTWC went through a couple of cycles of upgrading the development
potential and then downgrading it to poor. The circulation associated
with Tropical Disturbance 17 was very large--the MFR warning issued at
0600 UTC on 1 April noted that squally weather existed up to 750 nm from
the center in the western semi-circle and up to 300 nm on the eastern
side. Things began to look more hopeful for the system on 3 April. In
an interim STWO issued at 0700 UTC JTWC upgraded the development
potential to fair as deep convection began to consolidate over the LLCC.
MFR upgraded the system to a 30-kt tropical depression at 03/0600 UTC,
and at 1200 UTC Tropical Storm Isang was christened. The new tropical
storm was then centered about 500 nm east-northeast of Rodrigues Island.
B. Synoptic History
-------------------
After being upgraded to tropical storm status, Isang's track began to
trend more to the southwest as it moved around the western periphery of
the subtropical ridge to the southeast. The system remained at minimal
tropical storm intensity through 4 April, due in part to the inhibiting
influence of being located in an environment of drier air. Tropical
Storm Isang continued to track southwestward, reaching its point of
recurvature at around 1200 UTC on 5 April when it was located about
150 nm east-southeast of Rodrigues Island. As the storm turned toward
the south, the deep convection coupled vertically with the LLCC, leading
to an increase in the intensity. Isang reached its peak intensity of
60 kts at 1200 UTC on 6 April while located near 26.3S/67.0E, or about
465 nm southeast of Rodrigues. The storm by this time was moving off
toward the south-southeast at 17 kts into an environment of increasing
vertical shear and cold, dry air. Only twelve hours after reaching
its peak intensity, Isang was declared extratropical. The final warning
issued on Isang by MFR as the extratropical storm exited the agency's
AOR placed the center about 800 nm southeast of Rodrigues at 0600 UTC
on 7 April.
The minimum CP estimated by MFR was 975 hPa. JTWC's estimated peak
1-min avg MSW was 55 kts on 6 April. In an e-mail Karl Hoarau noted that
MFR later stated that Isang had briefly reached the tropical cyclone
stage around 0600 UTC on the 6th with the MSW (10-min avg) estimated at
65 kts, so it's possible Isang will be upgraded posthumously. A TRMM
85-GHz image taken at 06/0620 UTC shows a fairly well-defined eye
feature. It's very interesting that Isang's spurt of intensification
occurred at such a high latitude with the cyclone located in a seemingly
rather hostile environment.
A graphic displaying the track of Severe Tropical Storm Isang may be
found at the following link:
http://www.tropicalcyclone2005.com/database/tc_besttracks_graphics/INDIAN_SOUTHWEST/2005_17M-25S-ISANG_BT.gif>
C. Damage and Casualties
------------------------
There are no reports of any damage or casualties resulting from
Severe Tropical Storm Isang.
(Report written by Gary Padgett)
*************************************************************************
NORTHWEST AUSTRALIA/SOUTHEAST INDIAN OCEAN (AUW) - From 90E to 135E
Activity for April: 1 severe tropical cyclone
Sources of Information
----------------------
The primary sources of tracking and intensity information for
Northwest Australia/Southeast Indian Ocean tropical cyclones are
the warnings and advices issued by the Tropical Cyclone Warning
Centres at Perth, Western Australia, and Darwin, Northern Territory.
References to sustained winds imply a 10-minute averaging period
unless otherwise stated.
In the companion tropical cyclone tracks file, I occasionally
annotate positions from warnings issued by the Joint Typhoon Warning
Center (JTWC) of the U. S. Air Force and Navy, located at Pearl
Harbor, Hawaii, when they differ from the Australian centres' coor-
dinates by usually 40-50 nm or more. The JTWC warnings are also the
source of the 1-minute average maximum sustained wind values included
in the tracks file. Additionally, information describing details of
satellite imagery and atmospheric circulation features included in
the narratives is often gleaned from the JTWC warnings.
Northwest Australia/Southeast Indian Ocean
Tropical Activity for April
------------------------------------------
One tropical cyclone sprang to life in the Southeast Indian Ocean
east of 90E during April. Named Adeline by the Perth TCWC near the
Cocos Islands on 3 April, Adeline reached hurricane intensity the next
day as it chugged westward across the Indian Ocean. After crossing 90E
on the 5th, Adeline was renamed Juliet by Mauritius and eventually became
a very intense 120-kt cyclone as it recurved a couple hundred miles east
of Rodrigues Island. A report on Severe Tropical Cyclone Adeline-Juliet
follows.
VERY INTENSE TROPICAL CYCLONE ADELINE-JULIET
(MFR-18 / TC-26S)
1 - 14 April
----------------------------------------------------------------
Adeline: assigned by BoM Perth
Juliet: contributed by Zimbabwe
A. Storm Origins
----------------
The daily STWO issued by BoM Perth on 1 April mentioned a tropical
LOW which had formed roughly 385 nm east-northeast of the Cocos Islands.
The LOW was basically stationary and was given a high potential for
development into a tropical cyclone over the next couple of days. On
the same day JTWC issued an interim STWO for the same disturbance, noting
that convection was becoming increasingly organized over a possible LLCC
and that an upper-level analysis indicated favorable divergence aloft.
However, JTWC considered the chances for development over the next
24 hours to be poor. Due to the potential threat posed to the Cocos
Islands, BoM Perth began issuing tropical cyclone advices for the
islands, and high seas gale warnings were begun at 1600 UTC, indicating
that gales could develop within the next 18 to 24 hours.
B. Synoptic History
-------------------
Initially moving westward, the LOW turned to a southwesterly track
on the 3rd in the general direction of the Cocos Islands. The system
continued to exhibit increasing deep convection and improving outflow.
At 03/0700 UTC JTWC issued an interim STWO upgrading the potential for
development to fair, and at 1000 UTC BoM Perth upgraded the LOW to
Tropical Cyclone Adeline, located only about 25 nm east of the Cocos
Islands. As Adeline passed just to the south of the Cocos, its track
shifted to the west. The system continued to steadily intensify, with
the MSW reaching 55 kts by 1000 UTC on 4 April. (JTWC issued their
first warning on TC-26S at 04/1800 UTC, estimating the 1-min avg MSW
at only 35 kts, but issued an amended warning a few hours later upping
the winds to 55 kts.) At this stage Adeline was undergoing a spurt of
rapid intensification which carried the winds to hurricane force by
2300 UTC, at which time the cyclone was centered approximately 300 nm
west-southwest of the Cocos Islands.
Severe Tropical Cyclone Adeline continued to intensify as it headed
for longitude 90E--the boundary between Perth's AOR and that of Mauritius
and Meteo France La Reunion--with winds reaching 75 kts by 1000 UTC on
5 April. The 05/1000 UTC warning was the last issued by BoM Perth.
MFR issued their first warning on the cyclone at 1200 UTC as it was about
to cross the line of demarcation. Following the long-standing custom
in that part of the world, the Meteorological Service of Mauritius
renamed the storm Juliet with MFR referring to it as Tropical Cyclone
Juliet/ex-Adeline for a couple of days. Shortly after crossing into
the Southwest Indian Ocean basin proper, Adeline-Juliet underwent another
round of rapid intensification with winds reaching 105 kts at 0600 UTC
on 6 April. The intense cyclone's center was then located approximately
575 nm west of the Cocos Islands and moving westward at 8 kts. After
remaining at 105 kts for 24 hours, Juliet began to weaken a bit with the
MSW dropping to 80 kts by 1800 UTC on 7 August. The cyclone had also
turned to more of a west-southwesterly track, although it moved due
westward for an 18-hour period early on the 8th.
Tropical Cyclone Juliet began to re-intensify at 08/1800 UTC and
reached its peak intensity of 120 kts at 0000 UTC on 10 April when
located about 175 nm east-northeast of Rodrigues Island. The estimated
CP was a very low 905 hPa. Hurricane-force winds extended outward up
to 60 nm in the southern quadrants and gales covered an area over 350 nm
in diameter. (This wind radii information taken from MFR's warnings.)
The west-southwesterly track of the previous few days began to trend more
southwesterly as the very intense cyclone approached the small island.
The closest approach to Rodrigues occurred around 10/0600 UTC when
Juliet's center lay about 115 nm to the east-southeast.
After passing Rodrigues Juliet's track became increasingly southerly
and the cyclone began to steadily weaken as it entered an unfavorable
environment of drier air, increasing vertical shear and cooler SSTs.
The cyclone's point of recurvature was near 24.2S/63.4E at 1200 UTC
on 11 April. Winds were then estimated at 75 kts, but twelve hours
later MFR downgraded Juliet to a 60-kt tropical storm. An 11/1642 UTC
SSM/I image showed that the deep convection had become decoupled south-
east of the LLCC with cold, dry air entrained into the western semi-
circle. At 12/0600 UTC MFR classified the cyclone as an extratropical
storm, and at the same time JTWC issued their final warning. Ex-Juliet
by this time was moving southeasterly, and subsequently followed a track
slightly south of due east. The extratropical gale continued to weaken
and MFR issued the final bulletin at 14/1200 UTC with the 25-kt LOW
located around 1000 nm southeast of Rodrigues Island.
At Adeline-Juliet's first peak in intensity, JTWC estimated the peak
1-min avg MSW at 115 kts, which agrees well with MFR's 105 kts (10-min
avg). At the second and maximum peak at 10/0000 UTC, MFR estimated the
peak 10-min avg MSW at 120 kts. JTWC did not issue a warning at this
hour, but the previous one at 09/1800 UTC pegged the MSW at 130 kts
(1-min avg)--MFR's estimate at that time was 115 kts which is equivalent
to 130 kts 1-min avg.
A graphic displaying the track of Tropical Cyclone Adeline-Juliet
may be found at the following link:
http://www.tropicalcyclone2005.com/database/tc_besttracks_graphics/AUSTRALIA/2005_10U-18M-26S-ADELINE-JULIET_BT.gif>
C. Damage and Casualties
------------------------
No fatalities or damage are known to have resulted from Tropical
Cyclone Adeline-Juliet.
(Report written by Gary Padgett)
*************************************************************************
NORTHEAST AUSTRALIA/CORAL SEA (AUE) - From 135E to 160E
Activity for April: 1 possible tropical cyclone
Sources of Information
----------------------
The primary sources of tracking and intensity information for
Northeast Australia/Coral Sea tropical cyclones are the warnings
and advices issued by the Tropical Cyclone Warning Centres at
Brisbane, Queensland, and Darwin, Northern Territory, and on very
infrequent occasions, by the centre at Port Moresby, Papua New
Guinea. References to sustained winds imply a 10-minute averaging
period unless otherwise stated.
In the companion tropical cyclone tracks file, I occasionally
annotate positions from warnings issued by the Joint Typhoon Warning
Center (JTWC) of the U. S. Air Force and Navy, located at Pearl
Harbor, Hawaii, when they differ from the Australian centres' coor-
dinates by usually 40-50 nm or more. The JTWC warnings are also the
source of the 1-minute average maximum sustained wind values included
in the tracks file. Additionally, information describing details of
satellite imagery and atmospheric circulation features included in
the narratives is often gleaned from the JTWC warnings.
Northeast Australia/Coral Sea
Tropical Activity for April
-----------------------------
No tropical cyclones formed in BoM Brisbane's AOR during April, but
there was an interesting system near Papua New Guinea which very possibly
was a short-lived midget tropical cyclone. This system formed within
Port Moresby's area of warning responsibility and brought strong winds
well above gale force to Port Moresby and surrounding areas. The LOW
was not named as a tropical cyclone, but the Brisbane TCWC issued gale
warnings for the system, and the evidence strongly suggests that it was
a bona fide tropical cyclone. A report on this system, authored by Simon
Clarke, follows.
About a week after the above-mentioned system there was another LOW
in the Solomon Islands region which displayed some deep convection near
the center and could have been classified as a tropical depression.
However, the system was located in a region of moderate shear and never
became all that well-organized. BoM Brisbane mentioned this system in
their STWOs on 23 and 24 April.
PAPUA NEW GUINEA STORM
14-15 April
------------------------------------------
A. Synoptic History
-------------------
A tropical LOW first became apparent in the far northern Arafura Sea
on 12 April 2005. This LOW moved eastward close to the southern
coastline of Papua New Guinea from 13 to 16 April and may have
developed into a rare midget cyclone in the Torres Strait.
At 14/2230 UTC a gale warning was issued by BoM Queensland for a
developing LOW of 995 hPa near 9.3S/144.0E, or approximately 140 nm
northeast of Cape York, Queensland, and 160 nm west of Port Moresby,
Papua New Guinea. The Kumul Oil Search Marine Terminal at 8.1S/144.6E
recorded gusts to 55 knots as the system passed to the south.
The LOW moved eastward at approximately 10 kts and deepened to
993 hPa as the system developed deep convective banding over its western
quadrants. At 15/0308 UTC the LOW was 90 nm west of Port Moresby and
producing very rough seas and clockwise gales of 35-40 kts (and
possibly to 50 kts) within 60 nm of the centre.
However, as the LOW approached and interacted with the
southeastern landmass of Papua New Guinea and moved into a region of
increasing upper shear, it weakened and the final gale warning was
issued at 15/1854 UTC with the LOW near 10.5S/148.5S, or
approximately 120 nm east-southeast of Port Moresby. The LOW later
succumbed to strong northeasterly wind shear.
Jeff Callaghan advises that the Cairns, Queensland, BoM office
received calls from the public at Port Moresby since gales were being
experienced there. The Port Moresby office released a balloon at the
Port Moresby airport at 0000 UTC 15 April and the winds at 925 hPa
were 340/49 knots and at 894 hPa were 337/54 knots, which is
consistent with gales or worse in the Port Moresby area. A QuikScat
pass soon afterward depicted gales surrounding the LOW.
A graphic displaying the track of this system may be found at
the following link:
http://www.tropicalcyclone2005.com/database/tc_besttracks_graphics/PACIFIC_PNG/2005_00TS.gif>
B. Storm Effects
----------------
The following extract is taken from "The National" (15 April 2005):
"A STORM accompanied by strong winds wrecked havoc in Port Moresby on
Friday, causing major disruptions to electricity, communication and
airline flights.
"The heavy rain and winds brought down trees which blocked roads,
knocked down at least two power lines, and caused the Burns Peak
Repeater Site Tower to collapse, which disrupted communications.
"Four Air Niugini flights out of Port Moresby were also cancelled due
to bad visibility. According to an officer at the airlines customer
service, flights to Goroka, Lae, Rabaul and Mt. Hagen were cancelled due
to the bad weather and had to be rescheduled to the next day. PNG Power
issued a statement warning the public to stay away from fallen power
lines while the linesmen were busy all weekend trying to attend to the
fallen power lines. Telikom reported the collapse of its transmission
tower located at Burns Peak at about 11 AM which affected mobile
coverage, radio, and major business operations of Curtain Brothers, Napa
Oil Refinery and Atlas Steel and other essential services.
"In Port Moresby, the city was thrown into blackout as electricity
supply was cut off by fallen trees along various parts of the city while
the busy Port Moresby traffic was brought to crawling pace from heavy
flooding of the roads. In downtown Port Moresby, strong winds caused a
tree and a power pylon to collapse over a vehicle while at Koki Point
several passengers escaped with minor injuries when a power pylon
collapsed over a vehicle.
"A St. John Ambulance officer confirmed the incident but reported no
major harm to the passengers. The officer also reported that two
pedestrians were allegedly hit by a vehicle during the poor visibility
late Friday at Big Rooster in Boroko.
"As of yesterday afternoon, several residents were reportedly without
electricity supply after the disruptions on Friday. PNG Power issued a
statement saying workmen were still attending to fallen lines. The
general public in Port Moresby and surrounding areas are advised to treat
all fallen lines as still alive and report to PNG Power 24-hour services,
said Grant Hoffmeister, the acting Chief Executive Officer of PNG Power.
"Telikoms acting managing director Noel Mobiha also advised that
restoration of services may be delayed but every effort will be taken to
restore the services. In Daru, a duty policeman said two people were
swept out to the mainland by the strong winds but were recovered a day
later on the mainland."
(Report written by Simon Clarke with significant contributions by
Jeff Callaghan)
*************************************************************************
SOUTH PACIFIC (SPA) - South Pacific Ocean East of Longitude 160E
Activity for April: 3 tropical depressions
1 tropical cyclone of gale intensity
Sources of Information
----------------------
The primary sources of tracking and intensity information for
South Pacific tropical cyclones are the warnings and advisories
issued by the Tropical Cyclone Warning Centres at Nadi, Fiji (for
waters north of latitude 25S), and Wellington, New Zealand (for
waters south of latitude 25S). References to sustained winds imply
a 10-minute averaging period unless otherwise stated.
In the companion tropical cyclone tracks file, I occasionally
annotate positions from warnings issued by the Joint Typhoon Warning
Center (JTWC) of the U. S. Air Force and Navy, located at Pearl
Harbor, Hawaii, when they differ from the Southern Hemisphere
centres' coordinates by usually 40-50 nm or more. The JTWC warnings
are also the source of the 1-minute average maximum sustained wind
values included in the tracks file. Additionally, information
describing details of satellite imagery and atmospheric circulation
features included in the narratives is often gleaned from the JTWC
warnings.
South Pacific Tropical Activity for April
-----------------------------------------
Tropical activity returned to the South Pacific basin in April
following a month-long quiescence. No less than five systems were
numbered by RSMC Nadi, but only one was upgraded to tropical cyclone
status, and this was only for a brief period. Tropical Depression 15F
was upgraded to Tropical Cyclone Sheila on 22 April, but was maintained
as a tropical cyclone for only 12 hours. Another system, Tropical
Disturbance 16F, was apparently absorbed by Sheila during its brief
tenure as a named tropical cyclone. To the author's knowledge, TD-16F
was never classified as a tropical depression.
Three other systems were classified by Fiji as tropical depressions:
14F, 17F and 18F. Tropical Depression 14F was a very persistent system
which was mentioned in Nadi's Tropical Disturbance Summaries from the
14th of April until the first of May. The system was relocated several
times, and it's possible that the number was applied to more than one
weak LLCC embedded in the monsoon trough. TD-14F began well to the
northwest of Vanuatu, cruised around the islands of Vanuatu, then took
a Fiji vacation, and eventually wound up meandering around over the
waters between Fiji and Samoa.
Tropical Depression 17F occurred from 26 April to 1 May and spent its
lifetime basically meandering over waters north and north-northeast of
Vanuatu. The final and shortest-lived of the series, Tropical Depres-
sion 18F, formed on 29 April north of Fiji and moved southward, thence
jogging eastward, dissipating on 1 May just east of the Fijian islands.
Interestingly, all three depressions met their demise on 1 May and were
last mentioned in Nadi's 1800 UTC Tropical Disturbance Summary on that
date.
Graphics depicting the tracks of these tropical depressions may be
found at the following links:
http://www.tropicalcyclone2005.com/database/tc_besttracks_graphics/PACIFIC_FIJI/2005_14F_BT.gif>
http://www.tropicalcyclone2005.com/database/tc_besttracks_graphics/PACIFIC_FIJI/2005_17F_BT.gif>
http://www.tropicalcyclone2005.com/database/tc_besttracks_graphics/PACIFIC_FIJI/2005_18F_BT.gif>
TROPICAL CYCLONE SHEILA
(TD-15F)
20 - 23 April
-------------------------------------------
Tropical Cyclone Sheila was the ninth tropical cyclone to form in
the Southwest Pacific during the 2004/2005 season and the first in a
seven week gap since the previous cyclone in early March.
The initial LOW that developed into Sheila (TD-15F) was one in a
series of low-pressure centres (TD-14F, TD-16F and TD-17F) that were
part of a persistent monsoonal trough that extended from north of the
Solomon Islands to Fiji from as early as 16 April. The series of
depressions were located over SSTs of about 28-29 C. However, strong
upper-level northwesterly shear of 25-30 kts at the 250-hPa level
inhibited development of these systems until 21 April when TD-15's
LLCC became covered with convection close to its centre. Strong surface
westerly winds were established on TD-15's northern side, while a high-
pressure system over New Zealand provided a good southeasterly surge
to the south, providing the impetus for further development.
TD-15 moved to the southeast at 20 kts, running down the axis of
the South Pacific Convergence Zone as it was steered by northwesterlies
at middle levels. In doing so the depression moved along with the
upper-level flow and consolidated sufficiently to attain cyclone
status, being named Sheila at 22/0600 UTC near 18.4S/168.8W, or
approximately 65 nm northeast of Niue. Sheila passed to the near
north of TD-16 and wrapped this depression into its overall
circulation.
Sheila reached a peak intensity at 22/1200 UTC (CP of 990 hPa,
maximum 10-min avg winds of 40 kts) near 19.3S/166.4W. However,
Sheila continued to be a sheared cyclone with the LLCC soon becoming
exposed on the western edge of the CDO as winds at 250-hPa increased
to 45 kts. Cyclone status was lost at 22/1800 UTC near 20.2S/165.4W,
or approximately 240 nm east-southeast of Niue, only 12 hours after
being named.
The remnant extratropical LOW merged with a frontal system to the
south soon after.
A graphic displaying the track of Tropical Cyclone Sheila may be
found at the following link:
http://www.tropicalcyclone2005.com/database/tc_besttracks_graphics/PACIFIC_FIJI/2005_15F_SHEILA_BT.gif>
According to information sent by Huang Chunliang, during the
formative stages Nausori, Fiji (WMO 91683, 18.05S/178.57E) received
120.4 mm of rainfall during the 24 hours between 20/0000 and 21/0000
UTC.
Sheila passed close to the island of Niue where peak 10-min avg
winds of 33 kts were reported. However, it is not fully clear
whether or not these winds were associated with TD-16F rather than
Sheila. There were no reports of incidents associated with Sheila.
(Report written by Simon Clarke)
*************************************************************************
EXTRA FEATURE
In order to shorten the amount of typing in preparing the narrative
material, I have been in the habit of freely using abbreviations and
acronyms. I have tried to define most of these with the first usage
in a given summary, but I may have missed one now and then. Most of
these are probably understood by a majority of readers but perhaps a
few aren't clear to some. To remedy this I developed a Glossary of
Abbreviations and Acronyms which I first included in the August, 1998
summary. I don't normally include the Glossary in most months in
order to help keep them from being too long. If anyone would like to
receive a copy of the Glossary, please e-mail me and I'll be happy
to send them a copy.
*************************************************************************
AUTHOR'S NOTE: This summary should be considered a very preliminary
overview of the tropical cyclones that occur in each month. The cyclone
tracks (provided separately) will generally be based upon operational
warnings issued by the various tropical cyclone warning centers. The
information contained therein may differ somewhat from the tracking and
intensity information obtained from a "best-track" file which is based
on a detailed post-seasonal analysis of all available data. Information
on where to find official "best-track" files from the various warning
centers will be passed along from time to time.
The track files are not being sent via e-mail. They can be retrieved
from the archive sites listed below. (Note: I do have a limited e-mail
distribution list for the track files. If anyone wishes to receive
these via e-mail, please send me a message.)
Both the summaries and the track files are standard text files
created in DOS editor. Download to disk and use a viewer such as
Notepad or DOS editor to view the files.
The first summary in this series covered the month of October,
1997. Back issues can be obtained from the following websites
(courtesy of Michael Bath, Michael V. Padua, Michael Pitt, Chris
Landsea, and John Diebolt):
http://australiasevereweather.com/cyclones/>
http://www.typhoon2000.ph>
http://mpittweather.com>
ftp://ftp.aoml.noaa.gov/hrd/pub/landsea/padgett/>
http://www.tropicalcyclone2005.com/>
Another website where much information about tropical cyclones may
be found is the website for the UK Meteorological Office. Their site
contains a lot of statistical information about tropical cyclones
globally on a monthly basis. The URL is:
http://www.metoffice.gov.uk/weather/tropicalcyclone>
TROPICAL CYCLONE REPORTS AVAILABLE
JTWC now has available on its website the Annual Tropical Cyclone
Report (ATCR) for 2004 (2003-2004 season for the Southern Hemisphere).
ATCRs for earlier years are available also.
The URL is: http://199.10.200.33/jtwc.html>
Also, TPC/NHC has available on its webpage nice "technicolor"
tracking charts for the 2004 Atlantic and Eastern North Pacific
tropical cyclones; also, storm reports for all the 2004 Atlantic
and Eastern North Pacific cyclones are now available, as well as
track charts and reports on storms from earlier years.
The URL is: http://www.nhc.noaa.gov>
A special thanks to Michael Bath of McLeans Ridges, New South Wales,
Australia, for assisting me with proofreading the summaries.
PREPARED BY
Gary Padgett
E-mail: [email protected]
Phone: 334-222-5327
Kevin Boyle (Eastern Atlantic, Western Northwest Pacific, South
China Sea)
E-mail: [email protected]
John Wallace (Assistance with Eastern North Pacific)
E-mail: [email protected]
Huang Chunliang (Assistance with Western Northwest Pacific, South
China Sea)
E-mail: [email protected]
Simon Clarke (Northeast Australia/Coral Sea, South Pacific)
E-mail: [email protected]
*************************************************************************
*************************************************************************